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BEBR 

FACULTY  WORKING 
PAPER  NO.  1184 


UBRARY  OF  THE, 


NOV  1  9  1985 

UNivtKSlTY  OF  ILLINOIS 
\NA-CHAMPAIGN 


An  Adjustment  Procedure  for  Predicting 
Systematic  Risk 

Anil  K.  Bera 
Srinivasan  Kannan 


College  of  Commerce  and  Business  Administration 
Bureau  of  Economic  and  Business  Research 
University  of  Illinois,  Urbana-Champaign 


BEBR 


FACULTY  WORKING  PAPER  NO.  1184 
College  of  Commerce  and  Business  Administration 
University  of  Illinois  at  Urbana-Champaign 
September,  1985 


An  Adjustment  Procedure  for  Predicting  Systematic  Risk 


Anil  K.  Bera,  Assistant  Professor 
Department  of  Economics 

Srinivasan  Kannan,  Graduate  Assistant 
Department  of  Finance 


We  would  like  to  thank  Charles  Linke,  David  Whitford,  Kenton  Zumwalt, 
and  especially  Paul  Newbold  for  helpful  comments.   The  financial  support 
of  the  Research  Board  and  the  Bureau  of  Economic  and  Business  Research 
of  the  University  of  Illinois  is  gratefully  acknowledged. 


Digitized  by  the  Internet  Archive 

in  2011  with  funding  from 

University  of  Illinois  Urbana-Champaign 


http://www.archive.org/details/adjustmentproced1184bera 


AN  ADJUSTMENT  PROCEDURE  FOR  PREDICTING  SYSTEMATIC  RISK 

Abstract 

This  paper  looks  at  the  currently  available  beta  adjustment  tech- 
niques and  suggests  a  multiple  root-linear  model  to  adjust  for  the 
regression  tendency  of  betas.   Our  empirical  investigation  indicates 
that  cross-sectional  betas  are  not  normally  distributed  but  their 
distribution  tends  to  normal  after  a  square-root  transformation.   The 
multivariate  normality  observed  among  betas  after  the  transformation, 
makes  the  functional  form  of  our  model  correct.   Also,  we  observe  that 
the  disturbance  term  of  the  multiple  root-linear  model  passes  the 
tests  for  normality  and  homoscedasticity .   These  findings  make  the 
ordinary  least  squares  estimates  unbiased  and  efficient.   Finally,  the 
mean  square  errors  are  found  to  be  lower  when  our  adjustment  procedure 
is  used  vis-a-vis  the  existing  procedures. 


AN  ADJUSTMENT  PROCEDURE  FOR  PREDICTING  SYSTEMATIC  RISK 

Estimation  of  systematic  risk  is  one  of  the  important  aspects  of 
investment  analysis  and  has  attracted  the  attention  of  many  researchers. 
In  spite  of  substantial  contributions  in  the  recent  past  there  still 
remains  room  for  improvement  in  the  methodologies  currently  available 
to  forecast  systematic  risk.   This  paper  is  concerned  with  an  improved 
method  of  predicting  systematic  risk  for  individual  securities. 

The  central  model  in  most  of  the  research  pertaining  to  systematic 
risk  has  been  the  single  index  model: 

■«  =  °i +  siV  +  ht  (1) 

where  R.   and  R   are,  respectively,  the  random  return  on  security  i 
it      mt     »     r       j  y  j 

and  the  corresponding  random  market  return  in  period  t,  a.  and  g.  are 
the  regression  parameters   appropriate  to  security  i,  and  e.   is  the 

random  disturbance  term  with  E(e )  =  0.   One  of  the  many  assumptions 

2 
that  model  (1)  is  based  on  is  that  g .  is  constant  over  time.    In  his 

seminal  paper  Blume  [3]  observed  that  g.  was  changing  over  time  and 

there  was  a  regular  pattern  in  the  movement  which  he  termed  as  the 

regression  tendency  of  beta  coefficients.   Blume's  empirical  finding 

supported  the  hypothesis  that  over  time  betas  appear  to  take  less 

extreme  values  and  exhibit  a  tendency  towards  the  mean  value.   This 

would  mean  that  the  historical  betas  would  be  poor  estimators  of  the 

future  betas.   To  account  for  this  tendency  Blume  [3]  suggested  a 

regression  adjustment  procedure.   Alternatively,  Vasicek  [12]  proposed 

a  Bayesian  adjustment  technique  where  the  adjusted  beta  is  the  weighted 

average  of  the  historical  beta  and  the  mean  of  the  cross-sectional  betas. 


-2- 

Let  us  suppose  that  we  are  interested  in  predicting  the  betas  in 
period  t  and  let  fj   ,  be  the  historical  beta  in  period  (t-1).   The 
various  adjustment  procedures  described  above  can  be  put  in  the 
following  framework.: 


6ti  ■  dli  +  d2i6t-li  (2) 

where  &    .    denotes  the  predicted  value  of  beta  for  security  i  in  period 
t. 

(i)   Unadjusted  betas  are  obtained  by  substituting  d   =  0  and  d   =  1 
in  (2). 

A  A 

(ii)    Let   6,    and  6  ~    be    the   ordinary    least    squares    (OLS)    estimates 
obtained    by   estimating    the    linear    regression   model, 


t-1    =  61    +  626t-2   +  u  (3) 


where    u   is    the   disturbance    terra.      Now,    the   adjustment    procedure 
suggested    by    Blume    is    obtained    by    substituting   d        =  6-.    and 
d«.    =  5.    in    (2).      The    forecasting   model    can   be   written   as 


»tI  "  8t-i  +  «2(Bt-li  "  <W  (4) 


where  8   denotes  the  cross-sectional  mean  value  in  period  t. 
Blume's  hypothesis  is  clearly  reflected  in  (4).   In  each  period 

beta  shifts  towards  the  mean  and  the  amount  of  shift  is  propor- 

4 
tional  to  the  distance  of  beta  from  the  past  mean  value. 


■3- 


(iii)  The  adjustment  technique  suggested  by  Vasicek  involves  substi- 
tuting d, .  =8^  ,w.  and  d~  .  =  1  -  w.  in  (2)  with 
a      li    t-1  l      2i        l 

-  2 
bi  ,,.. 

wi  =  ~2 2  (5) 

sb  +  Sbi 

—  2 
where  s,   is  the  estimated  variance  of  the  cross-sectional  betas 
b 

2 
in  period  (t-1)  and  s.  .   is  the  estimated  variance  of  8   -,  .  . 
v  bi  t-li 

Here  we  should  note  that  for  Vasicek' s  adjustment  the  coefficients 
d  .  and  d    in  (2)  are  different  for  each  security,  whereas  MLPFS   and 
Blume's  adjustment  techniques  use  the  same  coefficients  for  all  the 
securities.   The  primary  purpose  of  all  these  approaches  is  the 
same  -  to  shrink  the  beta  values  towards  their  mean.   While  in  Blume's 
method  the  amount  of  shrinkage  depends  only  on  how  far  the  historical 
beta  is  away  from  the  average  value,  Vasicek's  method,  in  addition, 
takes  into  account  the  precision  of  the  historical  betas.   Blume  ([4], 
p.  789)  justifies  the  regression  line  (3)  by  assuming  that  8  _-,  and 
8   «  are  bivariate  normal.   Vasicek's  Bayesian  estimation  uses  a  normal 
prior  for  beta.   We  test  the  validity  of  these  normality  assumptions  in 
the  next  section. 

Now  let  us  look  at  an  implication  of  the  hypothesis  that  low  betas 
exhibit  an  increasing  tendency  and  high  betas  exhibit  a  decreasing  ten- 
dency over  time.   If  we  consider  the  scatter  diagram  in  the  (8  _9,8   -,) 
plane,  observations  corresponding  to  low  values  of  8  _7  should  in 
general  lie  above  the  line  8     =  6     and  observations  corresponding 
to  high  values  of  8  _9  should  in  general  lie  below  the  line.    Equation 
(3)  implies  that  the  extreme  values  of  beta  which  are  on  either  side  of 
but  equidistant  from  the  mean  will  shift  by  equal  amounts.   This  may 


-4- 

not  always  be  true.   Actually  Blume's  ([3],  p.  8)  evidence  shows  that 
the  regression  tendency  towards  the  mean  is  stronger  for  lower  values 
of  beta  than  for  higher  values.   This  suggests  that  rather  than  a 
linear  regression,  a  nonlinear  relationship  such  as 

6  7  U 

6t-l  =  6l6t-2  e  (6) 

where  6  ,',5.-,  >  0,  may,  perhaps  capture  the  regression  tendency  better. 
Equation  (6)  leads  to  a  log-linear  regression 

log  3t-1  -  6X   +  62  log  6t_2  +  u  (7) 

where  6,  =  log  6  1    and  u  is  now  the  additive  disturbance  terra.   Both  the 
linear  and  the  log-linear  regressions  are  special  cases  of  the 
following  general  regression  model: 

6t_1(X)  -  61   +  628t_2U)  +  u  (8) 

BX  -  1 
where  8(A)  =  - — is  the  Box-Cox  [5]  transformation.   When  A  =  1  we 

A 

obtain  the  linear  regression  model  and  when  A  *  0  equation  (8)  reduces 
to  Che  log-linear  model.   The  Box-Cox  transformation  might,  in  addition 
to  correcting  any  functional  misspecif ication  present  in  model  (3), 
push  the  distribution  of  transformed  variables  towards  normality.   In 
section  II  we  try  to  find  a  suitable  data  transformation  under  the  Box- 
Cox  framework.   Another  way  to  generalize  the  model  (3)  would  be  to 
include  some  extra  variables.   A  natural  step  is  to  include  betas  from 
an  additional  lag  period;  for  example,  we  may  consider 


3t-l    =5i   +626t-2   +638C-3  +  u  W 


-5- 

where  we  would  expect  69  >  So*   We  discuss  this  multiple  regression 
tendency  and  look,  at  some  empirical  evidence  in  Section  III. 

No  matter  how  good  a  model  is  to  explain  g   . ,  its  usefulness 
lies  in  predicting  g  ,  the  future  betas.   Earlier  studies  by  Klerakosky 
and  Martin  [10],  and  Eubank  and  Zumwalt  [7]  indicate  that,  taking  mean 
square  error  (MSE)  as  a  criterion,  there  is  very  little  difference 
between  Blume's  and  Vasicek's  adjustment  techniques  and  they,  in 
general,  outperform  MLPFS  technique  and  unadjusted  betas.   Results  of  a 
comparative  study  on  the  performance  of  the  adjustment  procedures 
suggested  by  us  vis-a-vis  Blume's  and  Vasicek's  techniques  are  reported 
in  Section  IV.   In  the  last  section  we  summarize  our  findings  and  make 
some  concluding  remarks. 

I.   Sampling  Properties  of  Beta 

Monthly  observations  on  R.  and  R  were  obtained  from  the  CRSP 

l      m 

tapes.    The  time  span  considered  was  from  July  1948  through  June  1983 
and  this  was  divided  into  seven  non-overlapping  estimation  periods  of 
sixty  months  each.   Using  model  (1)  beta  coefficients  for  individual 
securities  were  estimated  in  all  the  seven  periods  and  some  selected 
sample  statistics  for  these  estimates  have  been  reported  in  Table  I. 
As  expected  the  means  of  the  cross-sectional  betas  are  all  very 

Q 

close  to  unity  and  the  standard  deviations  are  around  0.45.    The  last 
three  columns  of  Table  I  are  concerned  with  the  normality  of  betas.   It 
can  be  seen  that  the  empirical  distributions  of  betas  are  positively 


-6- 

skewed  and  often  platykurtic.   The  following  test  statistic  which  com- 
bines the  skewness  and  kurtosis  measures  was  used  for  testing  nor- 
mality of  betas: 


2  2 

(skewness)     (kurtosis  -  3) 


24 


where  N  is  the  sample  size  (see  Bera  and  Jarque  [1]).    The  values  of 
the  statistic  have  been  reported  in  the  last  column.   The  null 
hypothesis  that  betas  are  normally  distributed,  is  overwhelmingly 
rejected  in  all  the  seven  periods.10   Since  the  betas  are  not  uni- 
variate normal  in  any  of  the  periods,  the  possibility  of  bivariate 
normality  of  betas  from  any  two  consecutive  periods  can  be  ruled  out. 
These  empirical  findings  cast  some  doubt  on  the  validity  of  both 
Blume's  and  Vasicek's  procedures. 


II.   Simple  and  Nonlinear  Regression  Tendency 
In  order  to  decide  the  nature  of  the  regression  tendency,  we  con- 
sidered the  equations  (3),  (7),  and  (8).   We  refer  to  these  three  as  the 
'linear',  'log-linear',  and  'Box-Cox'  models  respectively.   We  estimated 
these  three  models  for  t  =  3,4,5,6  and  7.   One  of  the  important  results 
we  obtained  was  that  the  estimates  of  lambdas  from  the  Box-Cox  regres- 
sions were  around  0.5.   This  could  imply  that  a  Box-Cox  model  with 
X  =  0.5 ,  i.e.  , 


/B^  -  «x  +«2/Bt.2+  u 


(10) 


-7- 

would  be  more  appropriate.    We  refer  to  equation  (10)  as  the  'root- 
linear'  model.   This  model  was  also  estimated  for  the  above  mentioned 

values  of  t.   The  results  of  the  various  regressions  have  been  reported 

12  2 

in  Table  II.     The  coefficient  of  determination  (R  )  values  are  not 

2 
very  high.   It  must  be  noted  that  the  R  values  for  different  models 

are  not  comparable  since  the  dependent  variables  are  different.   In  the 
case  of  the  linear  model  the  t-statistics  on  slope  and  the  intercept 
are  highly  significant.   However,  the  regression  coefficients  vary 
drastically  from  one  estimation  period  to  another  indicating  instability 
in  the  regression  tendency.   This  is  true  for  all  the  four  models. 
Next  we  looked  at  the  normality  of  the  disturbance  term.   While  nor- 
mality was  rejected  in  all  the  regressions  with  the  linear  and  the  log- 
linear  models,  it  was  accepted  in  all  but  one  of  the  regressions  with 
the  root-linear  model.   This  implies  that  the  OLS  estimates  are  effi- 
cient when  we  use  the  root-linear  model,  assuming  that  the  functional 
form  is  well  specified  and  there  is  no  heteroscedastici ty .   Also,  these 
results  led  us  to  the  conjecture  that  even  though  betas  were  not  nor- 
mally distributed,  the  square-root  transformation  could  probably  make 

13 
them  normal  while  the  log-transformation  would  not.     To  verify  this 

we  applied  the  normality  test  on  log-betas  and  root-betas.   The  out- 
comes have  been  reported  in  Table  III.   The  numbers  are  quite 
striking.   The  log-transformation  makes  the  distribution  more  skewed 
but  negatively,  and  the  moderate  platykurtosis  changes  to  strong  lep- 
tokurtosis.   As  a  result  the  problem  of  non-normality  becomes  more 


-8- 

acute.   With  the  square-root  transformation,  on  the  other  hand,  the 
values  of  skewness  and  kurtosis  change  in  such  a  way  that  the  nor- 
mality hypothesis  can  be  accepted  at  10%  and  1%  significance  levels, 
in  four  out  of  seven  periods.   Also,  the  values  of  the  test  statistic 
in  the  remaining  three  periods  are  not  much  above  the  critical  value. 
Given  these  results  it  may  not  be  irrational  to  conclude  that  betas 
follow  a  'root-normal*  distribution,  i.e.,  square  root  of  the  variable 

is  normal.     Of  course  this  does  not  mean  that  /$„  ,  and  /8   ,  . 

t-i       t-Z  m 

equation  (10)  are  jointly  normally  distributed. 

ill.   Multiple  Regression  Tendency 
By  examining  the  betas  over  the  seven  time  periods,  we  noticed  that 
the  regression  tendencies  were  rather  fuzzy.   For  example,  the  tendency 
to  decrease  or  to  increase  persisted  even  after  crossing  the  cross- 
sectional  mean  values.   Often  the  extreme  beta  values  did  not  move 
towards  the  grand  mean  in  the  next  period  but  did  so  in  the  period 
after.   Such  empirical  observations  implied  that  the  tendency  from 
period  (t-2)  to  (t-1)  was  not  the  best  estimate  of  the  tendency  from 
period  (t-1)  to  (t).   An  alternative  possibility  is  to  include  more 
'lags'  in  the  model.   This  has  an  intuitive  appeal  since  the  regression 
tendency  could  be  spread  over  more  than  just  the  previous  and  current 
periods.   To  test  this  hypothesis  we  decided  to  work  with  model  (9), 
which  we  refer  to  as  the  'mult«iple  linear'  (ML)  model.   Also,  given  the 
success  of  the  'root-linear'  model,  we  considered  the  'multiple  root- 
linear'  (MRL)  model: 


/B 


t-1  =  51  +  62  /6t-2  +  63  /6t-3  +  u  (Ii) 


-9- 


Results  from  the  regressions  using  (9)  and  (11)  are  given  in  Table  IV. 

2 
The  R  values  for  the  two  regressions  are  low  and  are  not  directly  com- 
parable to  those  in  Table  II  since  the  sample  sizes  are  different.   In 
both  the  multiple  regressions,  the  slope  coefficients  and  the  intercepts 
are  highly  significant.   We  expected  the  coefficient  on  lag  1  (69)  to 
be  greater  than  the  coefficient  on  lag  2  (6^),  since  we  felt  that 
information  from  the  immediate  past  should  have  more  bearing  on  the 

current  betas  than  information  from  the  distant  past.   Empirically  this 

16 
is  found  to  be  true  in  all  the  periods  for  both  the  regression  models. 

To  evaluate  the  two  models,  we  tested  for  normality  and  homosce- 
dasticity   of  the  disturbance  terms.   The  values  of  the  test  statistics 
are  in  Table  IV.   Both  the  models  pass  the  test  for  homoscedasticity  in 
three  out  of  four  cases  with  the  MRL  model  being  marginally  better  than 
the  ML  model.   The  fundamental  difference  between  the  two  models  is 
revealed  by  the  normality  test  statistic.   For  the  MRL  model  the  nor- 
mality of  the  disturbance  term  is  accepted  in  all  the  four  estimation 
periods  at  5%  level  of  significance;  however,  for  the  ML  model  we 
strongly  reject  the  normality  hypothesis  in  all  four  periods. 

To  conclude,  among  all  the  models  that  we  have  considered  so  far, 
the  MRL  model  captures  the  regression  tendency  best.   Of  course  this 
does  not  necessarily  mean  that  betas  adjusted  on  the  basis  ot  the  MRL 
model  would  be  the  best  in  forecasting.   A  comparative  study  is  needed 
to  evaluate  the  performance  of  different  adjustment  procedures  and 
this  we  do  in  the  next  section. 


-10- 

IV.   Performance  of  Different  Adjustment  Procedures 
For  this  study  we  considered  the  unadjusted  betas  and  the  betas 

obtained  using  Vasicek,  Blume,  log-linear,  root-linear,  ML  and  MRL 

18 
adjustment  techniques.     The  criterion  used  for  comparison  was  Mean 

Square  Error  (MSE)  given  by 

N 
MSE  "  N  .\     (Ai  "  V 

1  =  1 

where  A.s  are  the  actual  estimates  of  beta  in  period  t,  P.s  are  the 
l  l 

predicted  values  of  beta  using  a  particular  technique,  and  N  is  the 
number  of  securities  for  which  predictions  were  made.   Following 
Klemkosky  and  Martin  [10]  we  decomposed  the  MSE  into  three  components, 
namely,  bias,  inefficiency,  and  random  error.   The  results  have  been 
reported  in  Table  V.   The  ML  model  outperforms  Blume' s  technique  in  all 
the  periods  and  the  MRL  model  does  the  same  in  all  but  one  period. 
Also,  the  MRL  model  performs  better  than  the  simple  root-linear  model 
in  all  the  periods.   However,  in  terms  of  MSE  there  is  very  little  to 
choose  between  the  MRL  and  the  ML  models.   Both  these  models  outperform 
Vasicek's  adjustment  and  as  expected  all  the  adjusted  betas  do  better 
than  the  unadjusted  betas. 

Given  these  results  and  the  acceptance  of  normality  of  the  distur- 
bance term  in  model  (11),  the  choice  of  MRL  model  over  ML  model  seemed 
reasonable.   To  further  justify  this  choice  we  decided  to  examine  the 


trivariate  normality  of  /g  _. ,  /g   «,  and  /g  _~  [see  footnote  15].   The 

test  was  performed  for  both  betas  and  root-betas  using  the  test 

19 
statistic  developed  by  Bera  and  John  [2].     The  results  are  in  Table 

VI.   As  anticipated  we  rejected  the  joint  normality  of  betas  (recall 


-11- 

that  the  univariate  normality  had  been  rejected  in  all  time  periods). 
In  the  case  of  root-betas  we  rejected  the  joint  normality  hypothesis 
only  in  two  periods.   Even  in  these  two  cases  the  test  statistic  was 
much  smaller  than  that  obtained  for  the  actual  betas.   To  summarize, 
model  (11)  has  a  well  justified  functional  form  with  a  disturbance  term 
that  is  both  normal  and  homoscedastic.   Therefore,  the  OLS  estimates 
will  be  unbiased  and  efficient.   Moreover,  this  model  leads  to  a 
reduction  in  MSE.   Hence,  the  adjustment  technique  using  the  multiple 
root-linear  model  is  definitely  a  major  improvement  over  currently 
available  techniques. 

V.   Summary  and  Conclusions 
In  this  paper  we  have  provided  empirical  evidence  that  betas 
obtained  from  the  single  index  model  are  not  normally  distributed,  but 
become  normal  after  the  square-root  transformation.   This  finding 
suggests  that  the  adjustment  techniques  proposed  by  Blume ,  and  Vasicek 
may  not  always  be  appropriate.   On  the  other  hand,  the  joint  normality 
of  the  root  betas,  observed  in  several  periods,  together  with  the 
normality  and  homoscedasticity  of  the  disturbance  term  shows  that  the 
multiple  root-linear  model  is  quite  suitable.   Also,  with  mean  square 
error  as  a  criterion  the  adjustment  technique  suggested  by  us  performs 
better  than  the  other  techniques.   Our  model  can  be  extended  by 
including  some  firm-specific  variables.   Also,  further  investigation 
is  necessary  to  determine  the  optimal  lag-length. 


-12- 

FOOTNOTES 

The  parameter  6 • >  called  beta,  measures  the  systematic  risk  of 

security  i  and  is  defined  as  Cov(R.,R  )/Var(R  ). 

1   m       m 

2 
Many  attempts  have  been  made  to  relax  this  assumption.   Fabozzi 

and  Francis  [8],  Sunder  [11],  and  others  have  tried  to  account  for  the 

variations  of  beta  over  time  by  treating  it  as  a  random  coefficient. 

3 
Some  straightforward  ways  to  adjust  beta  towards  the  average  value 

are  also  available.   One  such  technique  used  by  Merrill  Lynch,  Pierce, 

Fenner  &  Smith,  Inc.  (MLPFS)  is  a  particular  case  of  Vasicek's  Bayesian 

estimate,  where  the  variances  of  historical  betas  are  all  assumed  to  be 

equal. 

4 
It  can  be  observed  that  if  the  average  beta  increases  over  two 

periods  then  equation  (4)  assumes  that  this  trend  will  persist  in  the 

next  period  also.   This  may  not  be  realistic.   Elton  and  Gruber  [6] 

suggest  that  by  applying  a  mean-correction  to  the  betas  obtained  using 

BLume's  adjustment  the  forecasts  could  be  improved. 

MLPFS  beta  estimates  are  easily  obtained  from  equation  (4)  by 
putting  et_1  =  8t_2  =  1,  i.e., 

h± =  l  +  6V6t-ii  - L)- 

Therefore,  the  performances  of  MLPFS  and  Blume's  techniques  can  be 
expected  to  be  close  whenever  the  average  value  of  betas  is  close  to 
unity. 


For  R  we  have  used  the  value  weighted  return  series  including 


-13- 

The  'high'  and  'low'  values  are  relative  to  the  mean. 
7 
ordinary  dividends. 

Q 

These  statistics  are  similar  to  those  reported  by  Blume  [3J, 
although  his  time  span  was  different  (July  1926  through  June  1968)  and 
the  length  of  each  estimation  period  in  his  study  was  seven  years. 

9 
The  test  statistic  is  derived  using  the  Lagrange  multiplier  test 

principle  with  Pearson  family  of  distributions  as  alternatives,  and 

this  test  has  very  good  power  compared  to  other  tests  of  normality. 

Under  the  normality  hypothesis,  the  statistic  is  asymptotically 

2 
distributed  as  central  x   (Chi-square)  with  2  degrees  of  freedom. 

Given  our  large  sample  sizes  (see  column  2  of  Table  I)  we  can  safely 

apply  this  test.   The  asymptotic  critical  values  at  10%,  5%  and  I7a 

significance  levels  are,  respectively,  4.61,  5.99  and  9.21. 

Here  we  should  note  that  because  of  the  large  sample  size  the 
test  will  nave  very  high  power  and  consequently  a  slight  departure  from 
normality  will  result  in  the  rejection  of  the  normality  hypothesis. 

We  are  thankful  to  Paul  Newbold  for  pointing  this  out. 

12 

The  number  of  cases  is  less  than  those  reported  in  Table  I  since 

the  common  set  of  companies  between  any  two  periods  was  less  than  the 

number  of  companies  in  either  period. 

13 

Note  that  the  disturbance  terra  is  a  linear  combination  of  the 

dependent  and  indpendent  variables. 


-14- 

14 

This  at  first  sight  may  appear  questionable  since  the  root- 
transformation  is  defined  only  for  positive  betas  and  only  positive 
roots  have  been  considered.   Empirically,  about  7500  betas  were  esti- 
mated and  of  these  only  13  were  found  to  be  negative.   Also,  the 
empirical  mean  and  standard  deviation  of  root-betas  were  approximately 
1.03  and  0.22,  respectively.   For  a  normal  random  variable  with  the 
above  mean  and  standard  deviation,  the  probability  of  it  being  nega- 
tive is  less  than  8.3  x  10 

15 


If  >/8t_1    and  »/8t_2   are    bivariate   normal    then   E(/8      ,  |/g      ~)    = 


6,    +  5  j  ^8f_?   with   E(u)    =   0   in    (10).      This    will    ensure   unbiasedness    of 
the    0LS   estimates.      In   addition,    if    u  is    normally   distributed    and 
homoscedastic ,    estimates    will    be   efficient.      In   section    IV   we    test    the 
joint    normality   of    the    root-betas. 

1  fS 

It  may  be  interesting  to  investigate  the  problem  of  determining 

the  'lag-length' . 

To  test  for  homoscedastici ty  we  used  White's  [13J  test  since  it 

does  not  assume  any  specific  form  of  heteroscedasticity .   The  test 

2  2 

statistic  is  calculated  as  N*R  where  N  is  the  sample  size  and  R  is 

the  coefficient  of  determination  obtained  by  regressing  the  square  of 

the  residuals  on  all  second  order  products  and  cross-products  of  the 

original  regressors.   Under  homoscedastici ty,  the  test  statistic  is 

2 
asymptotically  distributed  as  central  x   with  5  degrees  of  freedom. 

The  critical  values  at  10%,  5%   and  1%  significance  levels  are  9.24, 

11.07  and  15.09,  respectively. 


-15- 

18 

It  should  be  noted  tnat  the  log-linear  and  the  root-linear  models 

would  forecast  log  Sr  and  /8t»  respectively,  and  not  3  .  As  pointed 
out  by  Granger  and  N'ewbold  [9 J  ,  the  residual  variance  was  taken  into 
account  by  us  in  obtaining  the  predicted  values  of  8  from  the  fore- 
casts of  log  B   and  /Bt« 

19 

The  test  statistic  is  a  generalization  of  the  test  noted  in  foot- 
note 9  and  is  derived  using  multivariate  Pearson  family  of  distributions 
Under  the  hypothesis  of  multivariate  normality  the  test  statistic  is 
asymptotically  distributed  as  central  x   with  6  degrees  of  freedom. 
The  critical  values  for  this  test  are  10.64,  12.59,  and  16.81  at  10%, 
5%  and  1%   significance  levels,  respectively. 


-16- 


REFERENCES 


1.  Anil  K.  Bera  and  Carlos  M.  Jarque.  "Model  Specification  Tests: 
A  Simultaneous  Approach."  Journal  of  Econometrics.  20  (1982), 
59-82. 

2.  Anil  K.  Bera  and  S.  John.   "Tests  for  Multivariate  Normality  with 
Pearson  Alternatives."   Communication  in  Statistics  -  Theory  and 
Methods.   12  (1983),  103-117. 

3.  Marshall  £.  Blume.   "On  the  Assessment  of  Risk."   Journal  of  Finance 
26  (March  1971),  1-10. 

4.  .   "Betas  and  Their  Regression  Tendencies."   Journal  of 

Finance.   30  (June  1975),  785-795. 

5.  Box,  G.  E.  P.,  and  D.  R.  Cox.   "An  Analysis  of  Transformations." 
Journal  of  the  Royal  Statistical  Society.   Series  B,  26  (1964), 
211-243. 

6.  Edwin  J.  Elton  and  Martin  J.  Gruber.   Modern  Portfolio  Theory  and 
Investment  Analysis.   Second  Edition.   John  Wiley  &  Sons,  1984, 
pp.  122-123. 

7.  Arthur  A.  Eubank,  Jr.  and  J.  Kenton  Zumwalt.   "An  Analysis  of  the 
Forecast  Error  Impact  of  Alternative  Beta  Adjustment  Techniques 
and  Risk  Classes."   Journal  of  Finance.   34  (June  1979),  761-776. 

8.  Frank  J.  Fabozzi  and  Jack  Clark  Francis.   "Beta  as  a  Random 
Coefficient."   Journal  of  Financial  and  Quantitative  Analysis.   13 
(March.  1978),  101-116. 

9.  Granger,  C.  W.  J.  and  P.  Newbold.   "Forecasting  Transformed 
Series."   Journal  of  the  Royal  Statistical  Society.   Series  B, 
38  (1976),  189-203. 

10.  Robert  C.  Klemkosky  and  John  D.  Martin.   "The  Adjustment  of  Beta 
Forecasts."   Journal  of  Finance.   30  (September  1975),  1123-1128. 

11.  Shyam  Sunder.  "Stationari ty  of  Market  Risk:  Random  Coefficients 
Tests  for  Individual  Stocks."  Journal  of  Finance.  35  (September 
1980),  883-896. 

12.  Oldrich  A.  Vasicek.   "A  Note  on  Using  Cross-Sectional  Information 
in  Bayesian  Estimation  of  Security  Betas."   Journal  of  Finance. 
28  (December  1973),  1233-1239. 

13.  rialbert  White.  "A  Heteroskedastici ty-Consistent  Covariance 
Matrix  Estimator  and  a  Direct  Test  for  Heteroskedastici ty. " 
Econometrica.   48  (May  1980),  817-838. 

D/302 


Table  I 


Summary  Statistics  of  Beta  Coefficients 


Number  of  Standard  Normality 

Period        Companies   Mean    Deviation    Skewness   Kurtosis    Test  Statistics 


7/48 

-  6/53 

910 

1.114 

0.441 

0.236 

2.697 

11.928 

7/53 

-  6/58 

938 

0.924 

0.434 

0.325 

2.701 

20.007 

7/58 

-  6/63 

923 

1.044 

0.377 

0.563 

3.244 

51.050 

7/63 

-  6/68 

956 

1.169 

0.494 

0.395 

4 

2.824 

26.094 

7/68 

-  6/73 

1056 

1.235 

0.478 

0.486 

2.845 

42.628 

7/73 

-  6/78 

1255 

1.160 

0.412 

0.590 

3.375 

80.164 

7/78 

-  6/83 

1208 

1.096 

0.465 

0.353 

2.836 

26.442 

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Table  III 
Normality  Test  of  Transformed  Betas 


Log 

Transformation 

Root 

Transformation 

Period 

Test 

Test 

Skewness 

Kurtosis 

Statistic 

Skewness 

Kurtosis 

Statistic 

7/48  - 

6/53 

-0.998 

4.333 

218.434 

-0.308 

2.816 

15.671 

7/53  - 

6/58 

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3.585 

141.133 

-0.239 

2.505 

18.506 

7/58  - 

6/b3 

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3.793 

75.400 

0.044 

2.937 

0.450 

7/63  - 

6/68 

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3.741 

130.844 

-0.162 

2.702 

7.719 

7/68  - 

6/73 

-0.672 

4.018 

125.077 

-0.013 

2.744 

2.913 

7/73  - 

6/78 

-0.477 

3.373 

54.867 

0.080 

2.915 

1.716 

7/78  - 

6/83 

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3.670 

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Table  VI 
Multivariate  Normality  Test  Statistics 


Period  Beta  Root-beta 

1,  2  and  3  90.71251  31.88872 

2,  3  and  4  130.48173  21.18911 

3,  4  and  5  106.57415  14.30298 

4,  5  and  6  124.25677  11.01903 

5,  6  and  7  131.86308  7.35194